The D-Region Absorption Product shown below addresses the operational impact of the solar X-ray flux and solar energetic proton (SEP) events on HF radio communication. Long-range communications using high frequency (HF) radio waves (3 – 30 MHz) depend on reflection of the signals in the ionosphere. Radio waves are typically reflected near the peak of the F2 layer (~300 km altitude), but along the path to the F2 peak and back the radio wave signal suffers attenuation due to absorption by the intervening D-Region ionosphere.

The D-Region Absorption Prediction model is used as guidance to understand the HF radio degradation and blackouts this can cause.

Current D-Layer Absorption Prediction from NOAA Space WX service (click image to view more)
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